The exemplary embodiments described herein relate generally to transistors and, more specifically, to the use of circuits implementing a sigmoid function for applications employing a single transistor type.
A sigmoid function is a mathematical function that has a sigmoid or symmetrical “S-shaped” curve. The sigmoid function may have particular applications as an activation function in a computational network to define the output of a node given one or more inputs to the node. In this capacity, the sigmoid function may be used to transform linear inputs to nonlinear outputs, bound an output to between 0 and 1 so that the output can be interpreted as a probability, and reduce the complexity for computation as compared to other types of activation functions.
Implementation of the sigmoid function, f(x)=1/(1+e−x), as an activation function is of particular interest in analog neural networks, where sigmoid thresholding units are used for evaluating the outputs of the neurons in the hidden layers (between the input and output layers) and/or the output layers themselves. When implementing the sigmoid function in semiconductor devices such as complementary metal oxide semiconductors (CMOSs), typically an amplifier or buffer unit (or an analog-to-digital converter in mixed signal circuits) is configured to produce the sigmoid function. However, such implementations are not directly transferrable to non-complementary transistors.